2-3 years into the previous generation is late 2007 to late 2008. Any developer that released a PC game based on the PS2 version (the two of them) didn't do it for performance reasons, just like the current cross-gen games or Gun on the original 360. I only see evidence of a stronger focus on multiplatform development and Steam's impact on the PC market, so let's go back to your original statements:
Saying that people with weaker PCs are "massively skewing" the hardware statistics is like saying people without a job are "massively skewing" the unemployment ratio. It creates an inaccurate picture of the market by ignoring data you don't like.
There are plenty of people playing those 'core' games with weak or old gaming PCs/laptops. If that wasn't the case, developers wouldn't take them into account while designing their game. What would be the point?